Pressure-sensitive adhesive sheet

ABSTRACT

The present invention realizes a display device or input device having excellent ultraviolet protection property for the touch panel, display element or the like, while retaining optical characteristics, even when a small amount of or no optical film is used. The pressure-sensitive adhesive sheet of the present invention has a total light transmittance of 85% or more, a light transmittance at a wavelength of 380 nm of 5% or less, and a haze of 3% or less. The pressure-sensitive adhesive sheet preferably includes a pressure-sensitive adhesive layer containing an acrylic polymer and a triazine-based ultraviolet absorber.

This application is a Continuation of application Ser. No. 13/628,897filed Sep. 27, 2012, which claims priority from JP 2011-216301 filedSep. 30, 2011; the contents of all of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a pressure-sensitive adhesive sheet.

2. Background Art

Recently, in various fields, display devices such as a liquid crystaldisplay (LCD) or an input device used by combining with the displaydevice, such as a touch panel, has been widely used. In the displaydevice or the input device, a pressure-sensitive adhesive tape or sheetincluding a pressure-sensitive adhesive layer is used for laminating anoptical member. For example, a transparent pressure-sensitive adhesivesheet is used for laminating the touch panel and various kinds ofdisplay members optical members (for example, see Patent Documents 1 to3).

The optical members used in such a display device or an input device maybe sometimes required to have ultraviolet absorbency (ultravioletprotection property, UV protection property) for the purpose of, forexample, preventing deterioration of a liquid crystal display due toultraviolet light.

An optical film containing an ultraviolet absorber is known as such anoptical member (see, for example, Patent Document 4).

Patent Document 1: JP 2003-238915 A

Patent Document 2: JP 2003-342542 A

Patent Document 3: JP 2004-231723 A

Patent Document 4: JP 2011-126986 A

SUMMARY OF THE INVENTION

In display devices or input devices, however, there are some cases whereno or only a small amount of optical film is used. In these cases, adisplay device or an input device is demanded to have more excellentultraviolet protection property for a touch panel, display element orthe like therein, while retaining optical characteristics thereof.

Accordingly, an object of the present invention is to realize a displaydevice or an input device including a touch panel, a display element orthe like, in which the display device or input device has excellentultraviolet protection property for the touch panel, display element orthe like, while retaining optical characteristics, even when a smallamount of or no optical film is used.

The inventors have made intensive studies and, as a result, have foundthat, when a pressure-sensitive adhesive sheet used on a touch panel, adisplay element or the like has a total light transmittance not lessthan a predetermined value, has a light transmittance at a wavelength of380 nm not more than a predetermined value, and has a haze not more thana predetermined value, the display device or an input device havingexcellent ultraviolet protection property for the touch panel, displayelement or the like, while retaining optical characteristics, can berealized, even in the case of using a small amount of or no opticalfilm. The present invention has been completed based on these findings.

The present invention provides a pressure-sensitive adhesive sheet,having: a total light transmittance of 85% or more; a lighttransmittance at a wavelength of 380 nm of 5% or less; and a haze of 3%or less.

The pressure-sensitive adhesive sheet preferably contains apressure-sensitive adhesive layer containing an acrylic polymer and atriazine-based ultraviolet absorber.

In the pressure-sensitive adhesive sheet, the acrylic polymer preferablycontains, as a monomer unit, at least one of an alkyl (meth)acrylatehaving a linear or branched alkyl group and an alkoxyalkyl(meth)acrylate.

In the pressure-sensitive adhesive sheet, a total of a proportion of thealkyl (meth)acrylate and a proportion of the alkoxyalkyl (meth)acrylateis preferably 30 wt % or more based on total monomer components (100 wt%) forming the acrylic polymer.

In the pressure-sensitive adhesive sheet, the acrylic polymer preferablycontains, as a monomer unit, a monomer containing a nitrogen atom in amolecule thereof.

In the pressure-sensitive adhesive sheet, a proportion of the monomercontaining a nitrogen atom in a molecule thereof is preferably 1 to 30wt % based on total monomer components (100 wt %) forming the acrylicpolymer.

In the pressure-sensitive adhesive sheet, the acrylic polymer preferablycontains, as a monomer unit, a monomer containing a hydroxyl group in amolecule thereof.

In the pressure-sensitive adhesive sheet, a proportion of the monomercontaining a hydroxyl group in a molecule thereof is preferably 0.5 to25 wt % based on total monomer components (100 wt %) forming the acrylicpolymer.

In the pressure-sensitive adhesive sheet, a content of thetriazine-based ultraviolet absorber is preferably 1 to 10 parts byweight relative to 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive sheet is preferably an opticalpressure-sensitive adhesive sheet.

The pressure-sensitive adhesive sheet of the present invention has theabove described constitution, and therefore lamination thereof onto atouch panel, a display element or the like makes it possible to realizea display device or an input device having excellent ultravioletprotection property (UV protection property) for the touch panel,display element or the like while retaining optical characteristics,even in the case of using a small amount of or no optical film.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing light transmittance in a wavelength range offrom 280 to 780 nm of pressure-sensitive adhesive sheets obtained inExample 1 and Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

The pressure-sensitive adhesive sheet of the present invention includesat least a pressure-sensitive adhesive layer. The pressure-sensitiveadhesive sheet of the present invention has a total light transmittanceof 85% or more, a light transmittance at a wavelength of 380 nm of 5% orless, and a haze of 3% or less.

In the present specification, the “pressure-sensitive adhesive sheet” ismeant to include a “pressure-sensitive adhesive tape”. In addition, thesurface of a pressure-sensitive adhesive layer in the pressure-sensitiveadhesive sheet may be called “pressure-sensitive adhesive surface”.

The pressure-sensitive adhesive sheet of the present invention may be adouble-sided pressure-sensitive adhesive sheet in which thepressure-sensitive adhesive surfaces are included in both surfaces ofthe pressure-sensitive adhesive sheet, or a single-sidedpressure-sensitive adhesive sheet in which the pressure-sensitiveadhesive surface is included in only one surface of thepressure-sensitive adhesive sheet.

Among them, the pressure-sensitive adhesive sheet of the presentinvention is preferably the double-sided pressure-sensitive adhesivesheet from the standpoint of laminating two members each other.

The pressure-sensitive adhesive sheet of the present invention may be a“substrateless type” pressure-sensitive adhesive sheet that does nothave a substrate (substrate layer), or may be a pressure-sensitiveadhesive sheet with a substrate. In the present specification, the“substrateless type” pressure-sensitive adhesive sheet may be called“substrateless pressure-sensitive adhesive sheet”, and thepressure-sensitive adhesive sheet with a substrate may be called“pressure-sensitive adhesive sheet with substrate”.

Among them, the pressure-sensitive adhesive sheet of the presentinvention is preferably a substrateless pressure-sensitive adhesivesheet, and more preferably a double-sided pressure-sensitive adhesivesheet consisting of a pressure-sensitive adhesive layer (especially thepressure-sensitive adhesive layer of the present invention describedlater) so that the pressure-sensitive adhesive sheet of the presentinvention does not limit the kind of adherend, member or the like andmay be used for with the lamination of a variety of adherends, membersor the like

The pressure-sensitive adhesive sheet of the present invention has atotal light transmittance of 85% or more, preferably 90% or more. Thetotal light transmittance, as used herein, means a total lighttransmittance in the visible range, which is a wavelength range of 400nm to 780 nm. The total light transmittance can be measured, forexample, by using a haze meter according to JIS K 7361-1.

The pressure-sensitive adhesive sheet of the present invention has ahaze of 3% or less, more preferably 1.5% or less. The haze can bemeasured, for example, by using a haze meter according to JIS K 7136.

The light transmittance at a wavelength of 380 nm of thepressure-sensitive adhesive sheet of the present invention is 5% orless, preferably 1% or less, and more preferably 0.5% or less. The lighttransmittance at a wavelength of 330 nm of the pressure-sensitiveadhesive sheet of the present invention is not particularly limited, butis preferably 5% or less, more preferably 1% or less, and still morepreferably 0.5% or less. These light transmittances can be measured, forexample, by using a haze meter according to JIS K 7361-1.

In particular, in the pressure-sensitive adhesive sheet of the presentinvention, the light transmittance in a whole wavelength range of 330 nmto 380 nm is preferably 5% or less, more preferably 1% or less, andstill more preferably 0.5% or less. The light transmittance in the wholewavelength range of 330 to 380 nm can be measured, for example, by usinga haze meter according to JIS K 7361-1.

The b* value of the pressure-sensitive adhesive sheet of the presentinvention is not particularly limited, but is preferably from 0 to 2.0,more preferably from 0 to 1.5. The pressure-sensitive adhesive sheet ofthe present invention having the b* value of 2.0 or less is less likelyto adversely affect the appearance of a product (especially, an opticalproduct described later) in which the pressure-sensitive adhesive sheetof the present invention is used, and therefore is preferred. The b*value is a b* value in the L*a*b* color system, which is according toJIS Z 8729, and can be measured by a simplified spectrophotometriccolorimeter (trade name “DOT-3C”, manufactured by Murakami ColorResearch Laboratory Co., Ltd.).

(1) Pressure-Sensitive Adhesive Layer

The pressure-sensitive adhesive sheet of the present invention includesat least a pressure-sensitive adhesive layer. In particular, thepressure-sensitive adhesive sheet of the present invention preferablyhas at least a pressure-sensitive adhesive layer that has a total lighttransmittance of 85% or more, a light transmittance at a wavelength of380 nm of 5% or less, and a haze of 3% or less. Incidentally, “apressure-sensitive adhesive layer that has a total light transmittanceof 85% or more, a light transmittance at a wavelength of 380 nm of 5% orless, and a haze of 3% or less” is herein sometimes referred to as “thepressure-sensitive adhesive layer of the present invention”. Also, apressure-sensitive adhesive layer of the present invention that is anacrylic pressure-sensitive adhesive layer is sometimes referred to as“the acrylic pressure-sensitive adhesive layer of the presentinvention”.

The pressure-sensitive adhesive layer of the present invention has atotal light transmittance of 85% or more, preferably 90% or more. Thetotal light transmittance can be measured, for example, by using a hazemeter according to JIS K 7361-1.

The pressure-sensitive adhesive layer of the present invention has ahaze of 3% or less, more preferably 1.5% or less. The haze can bemeasured, for example, by using a haze meter according to JIS K 7136.

The light transmittance at a wavelength of 380 nm of thepressure-sensitive adhesive layer of the present invention is 5% orless, preferably 1% or less, and more preferably 0.5% or less. The lighttransmittance at a wavelength of 330 nm of the pressure-sensitiveadhesive layer of the present invention is not particularly limited, butis preferably 5% or less, more preferably 1% or less, and still morepreferably 0.5% or less. These light transmittances can be measured, forexample, by using a haze meter according to JIS K 7361-1.

In particular, in the pressure-sensitive adhesive layer of the presentinvention, the light transmittance in a whole wavelength range of 330 nmto 380 nm is preferably 5% or less, more preferably of 1% or less, andstill more preferably of 0.5% or less. The light transmittance in thewhole wavelength range of 330 to 380 nm can be measured, for example, byusing a haze meter according to JIS K 7361-1.

The b* value of the pressure-sensitive adhesive layer of the presentinvention is not particularly limited, but is preferably from 0 to 2.0,more preferably from 0 to 1.5. The pressure-sensitive adhesive layer ofthe present invention having the b* value of 2.0 or less is less likelyto adversely affect the appearance of a product (especially, an opticalproduct described later) in which the pressure-sensitive adhesive layerof the present invention is used, and therefore is preferred. The b*value is a b* value in the L*a*b* color system, which is according toJIS Z 8729, and can be measured by a simplified spectrophotometriccolorimeter (trade name “DOT-3C”, manufactured by Murakami ColorResearch Laboratory Co., Ltd.).

The pressure-sensitive adhesive included in the pressure-sensitiveadhesive layer (in particular, the pressure-sensitive adhesive layer ofthe present invention) included in the pressure-sensitive adhesive sheetof the present invention is not particularly limited, and examplesthereof include acrylic pressure-sensitive adhesive, rubber-basedpressure-sensitive adhesive, vinyl alkyl ether-based pressure-sensitiveadhesive, silicone-based pressure-sensitive adhesive, polyester-basedpressure-sensitive adhesive, polyamide-based pressure-sensitiveadhesive, urethane-based pressure-sensitive adhesive, fluorine-basedpressure-sensitive adhesive, epoxy-based pressure-sensitive adhesive,etc. Among them, as the pressure-sensitive adhesive which constitutesthe pressure-sensitive adhesive layer, the acrylic pressure-sensitiveadhesive is preferable from the standpoint of weather resistance, costand easiness of design of pressure-sensitive adhesive. That is, thepressure-sensitive adhesive sheet of the present invention preferablyincludes the acrylic pressure-sensitive adhesive (in particular, theacrylic pressure-sensitive adhesive of the present invention) includingan acrylic polymer as a main component. These pressure-sensitiveadhesive may be used either alone or in combination of two or more kindsthereof.

The pressure-sensitive adhesive included in the pressure-sensitiveadhesive layer of the present invention may be a pressure-sensitiveadhesive having any form. Examples of the pressure-sensitive adhesiveincluded in the pressure-sensitive adhesive layer of the presentinvention include an emulsion type pressure-sensitive adhesive, asolvent type (solution type) pressure-sensitive adhesive, an activeenergy ray-curable pressure-sensitive adhesive, a hot melt typepressure-sensitive adhesive and the like. Of these, a solvent typepressure-sensitive adhesive and an active energy ray-curablepressure-sensitive adhesive are preferable from the standpoints ofproductivity and compatibility with the ultraviolet absorber.

The content of the acrylic polymer in the acrylic pressure-sensitiveadhesive is not particularly limited, and is preferably 70 wt % or more(for example, 70 to 100 wt %), and more preferably 85 wt % or more (forexample, 85 to 100 wt %) based on the whole amount of thepressure-sensitive adhesive (100 wt %).

(Acrylic Polymer)

The acrylic pressure-sensitive adhesive layer is preferably formed froman acrylic pressure-sensitive adhesive composition. The acrylicpressure-sensitive adhesive composition is not particularly limited, andexamples thereof include an acrylic pressure-sensitive adhesivecomposition that includes the acrylic polymer as an essential component,and an acrylic pressure-sensitive adhesive composition that includes, asan essential component, a mixture of monomers forming the acrylicpolymer (referred to as a “monomer mixture” in some cases) or partiallypolymerized product thereof. As the former acrylic pressure-sensitiveadhesive, examples thereof include a so-called solvent typepressure-sensitive adhesive composition, and as the latter acrylicpressure-sensitive adhesive, examples thereof include a so-called activeenergy-ray curable pressure-sensitive adhesive composition. The acrylicpressure-sensitive adhesive composition may include an additive, ifneeded.

The term “pressure-sensitive adhesive composition” as used hereinincludes a “composition for forming the pressure-sensitive adhesive”.The term “monomer mixture” as used herein means a mixture consisting ofonly monomer components forming the polymer. The term “partiallypolymerized product” as used herein means a composition where onecomponent or two or more components out of constituent components of themonomer mixture are partially polymerized.

The acrylic polymer is a polymer formed from a component including anacrylic monomer as an essential monomer component. As the monomercomponent of the acrylic polymer, a copolymerizable monomer may beincluded.

The acrylic polymer is preferably formed from (composed of) a monomercomponent including, as the essential monomer component, an alkyl(meth)acrylate having a linear or branched alkyl group and/oralkoxyalkyl (meth)acrylate. That is, the acrylic polymer preferablyincludes, as the monomer constituent unit, an alkyl (meth)acrylatehaving a linear or branched alkyl group and/or alkoxyalkyl(meth)acrylate. In this specification, the “alkyl (meth)acrylate havinga linear or branched alkyl group” may be simply referred to as a “alkyl(meth)acrylate”; and the “(meth)acryl” means “acryl” and/or “methacryl”(one or both of “acryl” and “methacryl”), and the same shall applyhereinunder. The acrylic polymer is formed from one or two or more kindsof the monomer component(s).

As the alkyl (meth)acrylate (alkyl (meth)acrylate having a linear orbranched alkyl group), examples thereof include an alkyl (meth)acrlyatehaving a liner or branched alkyl group having 1 to 20 carbon atoms, suchas methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate), pentyl(meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl(meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate,decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate,dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl(meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate,heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl(meth)acrylate, and eicosyl (meth)acrylate. Among them, alkyl(meth)acrylate having a linear or branched alkyl group having 1 to 12carbon atoms is preferable; and 2-ethylhexyl acrylate (2EHA), n-butylacrylate (BA) and methyl methacrylate (MMA) are more preferable. Thealkyl (meth)acrylate may be used either alone or in combination of twoor more thereof.

The alkoxyalkyl (meth)acrylate is not particularly limited, and examplesthereof include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl(meth)acrylate, methoxytriethylene glycol (meth)acrylate,3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate,4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate. Amongthem, as the alkokyalkyl (meth)acrylate, the alkoxyalkyl acrylate ispreferable, and 2-methoxyethyl acrylate (MEA) is more preferable. Thealkoxyalkyl (meth)acrylate may be used either alone or in combination oftwo or more thereof.

The total of the proportion of the alkyl (meth)acrylate and theproportion of the alkoxyalkyl (meth)acrylate [(proportion of alkyl(meth)acrylate)+(proportion of alkoxyalkyl (meth)acrylate)] based on thetotal monomer components (100 wt %) forming the acrylic polymer is notparticularly limited, but is preferably 30 wt % or more (for example,from 30 to 99 wt %), more preferably 50 wt % or more (for example, from50 to 99 wt %).

The ratio of the alkyl (meth)acrylate and the alkoxyalkyl (meth)acrylateis not particularly limited, but is preferably from 100:0 to 25:75, morepreferably from 100:0 to 50:50, in terms of the weight ratio of [theformer:the later].

The acrylic polymer may include a copolymerizable monomer as the monomercomponent. As the monomer constituent unit of the acrylic polymer, acopolymerizable monomer may be included.

Examples of the copolymerizable monomer preferably include, but notlimited to, a monomer containing a nitrogen atom in a molecule thereof,and a monomer containing a hydroxyl group in a molecule thereof in termsof providing a pressure-sensitive adhesive layer that exhibitssuppressed cloudiness and enhanced durability under high-humidityconditions, as well as good compatibility with an ultraviolet absorber.That is, the acrylic polymer preferably contains a monomer containing anitrogen atom in a molecule thereof as a monomer unit. Also, the acrylicpolymer preferably contains a monomer containing a hydroxyl group in amolecule thereof as a monomer unit.

The monomer containing a nitrogen atom in a molecule thereof has one ormore nitrogen atoms in its molecule (in one molecule thereof). In thisspecification, the “monomer containing a nitrogen atom in a moleculethereof” is called a “nitrogen atom-containing monomer” in some cases.The nitrogen atom-containing monomer may be used either alone or incombination of two or more thereof.

More particularly, examples of the nitrogen atom-containing monomerinclude N-vinyl cyclic amide, (meth)acryl amides and the like.

As the N-vinyl cyclic amide, examples thereof include an N-vinyl cyclicamide represented by the following formula (1).

(In the formula (1), R¹ represents a divalent organic group)

In the formula (1), R¹ is a divalent organic group, preferably adivalent saturated hydrocarbon group or a divalent unsaturatedhydrocarbon group, and more preferably a divalent saturated hydrocarbongroup (for example, an alkylene group having 3 to 5 carbon atoms and thelike).

Examples of the N-vinyl cyclic amide represented by the formula (1)include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone,N-vinyl-3-morpholinone, N-vinyl-2-caprolactam,N-vinyl-1,3-oxazine-2-one, N-vinyl-3,5-morpholine dione, and the like.

Examples of the (meth)acrylamides include (meth)acrylamide, N-alkyl(meth)acrylamide, N,N-dialkyl (meth)acrylamide and the like. Examples ofthe N-alkyl (meth)acrylamide include N-ethyl (meth)acrylamide,N-isopropyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-octylacrylamide and the like. Examples of the N-alkyl (meth)acrylamideinclude (meth)acrylamide having an amino group, such asdimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamideand dimethylaminopropyl (meth)acrylamide. Examples of the N,N-dialkyl(meth)acrylamide include N,N-dimethyl (meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl) (meth)acrylamide, N,N-di(t-butyl)(meth)acrylamide and the like.

The (meth)acrylamides also includes various N-hydroxyalkyl(meth)acrylamides. Examples of the N-hydroxyalkyl (meth)acrylamidesinclude N-methylol (meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl) (meth)acrylamide,N-(1-hydroxypropyl) (meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl) (meth)acrylamide,N-(3-hydroxybutyl) (meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide, N-methyl-N-2-hydroxyethyl (meth)acrylamide and thelike.

The (meth)acrylamides also includes variousN-alkoxyalkyl(meth)acrylamides. Examples of the N-alkoxyalkyl(meth)acrylamide include N-methoxymethyl (meth)acrylamide,N-butoxymethyl (meth)acrylamide and the like.

Examples of the nitrogen atom-containing monomer other than the N-vinylcyclic amide and the (meth)acrylamides include an amino group-containingmonomer such as aminoethyl (meth)acrylate, dimethylaminoethyl(meth)acrylate, dimethylaminopropyl (meth)acrylate and t-butylaminoethyl(meth)acrylate; a cyano group-containing monomer such as acrylonitrileand methacrylonitrile; a heterocyclic ring-containing monomer such as(meth)acryloyl morpholine, N-vinylpiperazine, N-vinylpyrrole,N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole,vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole,vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloyl pyrrolidine, (meth)acryloyl piperidine andN-methylvinylpyrrolidone; an imide group-containing monomer including amaleimide-based monomer such as N-cyclohexylmaleimide,N-isopropylmaleimide, N-laurylmaleimide and N-phenylmaleimide, anitaconimide-based monomer such as N-methylitaconimide,N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide,N-2-ethylhexylitaconimide, N-laurylitaconimide andN-cyclohexylitaconimide, a succinimide-based monomer such asN-(meth)acryloyloxymethylene succinimide,N-(meth)acryloyl-6-oxyhexamethylene succinimide andN-(meth)acryloyl-8-oxyoctamethylene succinimide; an isocyanategroup-containing monomer such as 2-(meth)acryloyloxyethyl isocyanate;and the like.

Among them, as the nitrogen atom-containing monomer, N-vinyl cyclicamide represented by the formula (1) and (meth)acrylamides arepreferable, N-vinyl-2-pyrrolidone (NVP), N-vinyl-2-caprolactam,N,N-dimethyl (meth)acrylamide and N,N-diethyl (meth)acrylamide are morepreferable, and N-vinyl-2-pyrrolidone is even more preferable.

The proportion of the nitrogen atom-containing monomer based on thetotal monomer components (100 wt %) forming the acrylic polymer is notparticularly limited, but is preferably from 1 to 30 wt %, morepreferably from 3 to 25 wt %, and still more preferably from 3 to 20 wt%, in terms of providing an acrylic pressure-sensitive adhesive layer ofhigh transparency by controlling the total light transmittance and thehaze of the acrylic pressure-sensitive adhesive layer, and providing apressure-sensitive adhesive layer having good compatibility with anultraviolet absorber.

The monomer containing a hydroxyl group in a molecule thereof has one ormore hydroxyl groups in its molecule (in one molecule thereof). However,in the monomer containing a hydroxyl group in a molecule thereof, thenitrogen atom-containing monomer is not included. That is, in thisspecification, the monomer containing both a nitrogen atom and ahydroxyl group in a molecule thereof is included in the “nitrogenatom-containing monomer”. In this specification, the “monomer containinga hydroxyl group in a molecule thereof” is called a “hydroxylgroup-containing monomer” in some cases. The hydroxyl group-containingmonomer may be used either alone or in combination or two or morethereof.

Examples of the hydroxyl group-containing monomer include hydroxylgroup-containing (meth)acrylic acid ester, such as 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl(meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl(meth)acrylate and (4-hydroxymethylcyclohexyl) (meth)acrylate; vinylalcohol, allyl alcohol and the like.

Among them, as the hydroxyl group-containing monomer, hydroxylgroup-containing (meth)acrylic acid ester is preferable, and2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) aremore preferable.

The proportion of the hydroxyl group-containing monomer based on thetotal monomer components (100 wt %) forming the acrylic polymer is notparticularly limited, but is preferably from 0.5 to 25 wt %, morepreferably from 1 to 20 wt %, and still more preferably from 5 to 20 wt%, in terms of providing an acrylic pressure-sensitive adhesive layer ofhigh transparency by controlling the total light transmittance and thehaze of the acrylic pressure-sensitive adhesive layer, and generating anappropriate cohesive force, thereby suppressing cohesive failure.

As the copolymerizable monomer other than the nitrogen atom-containingmonomer and hydroxyl group-containing monomer, a polyfunctional monomermay also be used. As the polyfunctional monomer, examples thereofinclude hexanediol di(meth)acrylate, butanediol di(meth)acrylate,(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycoldi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, trimethylolpropane tri(meth)acrylate,tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxyacrylate, polyester acrylate andurethane acrylate. The polyfunctional monomer may be used either aloneor in combination of two or more thereof.

The content of the polyfunctional monomer is not particularly limited,but is preferably 0.5 wt % or less (for example, 0 wt % to 0.5 wt %) andmore preferably 0 wt % to 0.1 wt % based on the total monomer components(100 wt %) forming the acrylic polymer.

In addition, examples of the copolymerizable monomer include: an epoxygroup-containing monomer (for example, glycidyl (meth)acrylate,methylglycidyl (meth)acrylate and the like); a sulfonategroup-containing monomer (for example, sodium vinyl sulfonate and thelike); a phosphate group-containing monomer; (meth)acrylic acid esterhaving an alicyclic hydrocarbon group (for example, cyclopentyl(meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate andthe like); (meth)acrylic acid ester having an aromatic hydrocarbon group(for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl(meth)acrylate and the like); vinyl esters (for example, vinyl acetate,vinyl propionate and the like); an aromatic vinyl compound (for example,styrene, vinyl toluene and the like); olefins or dienes (for example,ethylene, propylene, butadiene, isoprene, isobutylene and the like);vinyl ethers (for example, vinyl alkyl ether and the like); vinylchloride, and the like.

The acrylic polymer can be prepared by polymerizing the monomercomponents. The polymerization method of the acrylic polymer is notparticularly limited, and examples thereof include a solutionpolymerization method, an emulsion polymerization method, a bulkpolymerization method and a polymerization method by an activeenergy-ray irradiation (active energy-ray polymerization method). Amongthem, from the standpoint of transparency and cost of thepressure-sensitive adhesive layer, the solution polymerization methodand the active energy-ray polymerization method are preferable, and thesolution polymerization method is more preferable.

In the polymerization of the acrylic polymer, various kinds of generalsolvents can be used. Examples of such a solvent include organicsolvents such as: esters such as ethyl acetate and n-butyl acetate;aromatic hydrocarbons such as toluene and benzene; aliphatichydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons suchas cyclohexane and methylcyclohexane; and ketones such asmethylethylketone and methylisobutylketone. The solvents may be usedeither alone or in combination of two or more thereof.

In the polymerization of the acrylic polymer, a polymerization initiatorsuch as a thermal polymerization initiator or a photopolymerizationinitiator (photoinitiator) may be used depending on a kind ofpolymerization reaction. The polymerization initiator may be used eitheralone or in combination of two or more thereof.

Examples of the thermal polymerization initiator include an azo-basedinitiator, a peroxide-based polymerization initiator (for example,dibenzoyl peroxide, tert-butylpermaleate and the like), a redox-basedpolymerization initiator and the like. Among the initiators, anazo-based initiator as disclosed in JP 2002-69411 A is particularlypreferable. As the azo-based initiator, examples thereof include2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis-2-methylbutyronitrile(AMBN), dimethyl 2,2′-azobis(2-methylpropionate),4,4′-azobis-4-cyanovaleric acid and the like.

The used amount of the azo-based initiator is not particularly limited,and is preferably 0.05 parts by weight to 0.5 parts by weight, and morepreferably 0.1 parts by weight to 0.3 parts by weight, based on 100parts by weight of the total amount of the monomer components formingthe acrylic polymer.

The weight average molecular weight (Mw) of the acrylic polymer is notparticularly limited, and is generally 100,000 to 3,000,000, preferably300,000 to 1,500,000, and more preferably 500,000 to 1,100,000 from thestandpoint of the coating property of the acrylic pressure-sensitiveadhesive composition including acrylic polymer.

(Ultraviolet Absorber)

The pressure-sensitive adhesive layer (especially, the acrylicpressure-sensitive adhesive layer of the present invention) preferablycontains an ultraviolet absorber (UVA) in terms of providing highultraviolet absorbency by controlling the light transmittance at awavelength of 380 nm. Examples of the ultraviolet absorber preferablyinclude, but not limited to, a benzotriazole-based ultraviolet absorber,a benzophenone-based ultraviolet absorber and a triazine-basedultraviolet absorber. The ultraviolet absorbers may be used alone or incombination of two or more kinds thereof.

Among them, the ultraviolet absorber is preferably a triazine-basedultraviolet absorber, more preferably a hydroxyl group-containingtriazine ultraviolet absorber, and still more preferably a hydroxyphenyltriazine ultraviolet absorber, in terms of the ultraviolet absorbency,as well as in terms of exhibiting high compatibility with an acrylicpolymer and of easily providing a acrylic pressure-sensitive adhesivelayer having high transparency by controlling the total lighttransmittance and the haze of the acrylic pressure-sensitive adhesivelayer. That is, the pressure-sensitive adhesive sheet of the presentinvention preferably includes a pressure-sensitive adhesive layer thatcontains the above-mentioned acrylic polymer and the triazine-basedultraviolet absorber (especially, hydroxyphenyl triazine ultravioletabsorber).

Examples of the triazine-based ultraviolet absorber include, but notlimited to, 2,4-diphenyl-6-(2-hydroxy-4-methoxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-ethoxyphenyl)-1,3,5-triazine,2,4-diphenyl-(2-hydroxy-4-propoxyphenyl)-1,3,5-triazine,2,4-diphenyl-(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-dodecyloxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-benzyloxyphenyl)-1,3,5-triazine,2,4-diphenyl-6-(2-hydroxy-4-butoxyethoxy)-1,3,5-triazine,2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-methoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-etoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-propoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-dodecyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-benzyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-ethoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-butoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-propoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-methoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-propoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-hexyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-octyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-dodecyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-benzyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-butoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-propoxyethoxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine,2,4,6-tris(2-hydroxy-3-methyl-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine.

Furthermore, a commercially available product can be used as thetriazine-based ultraviolet absorber. Examples thereof include “TINUVIN400” (manufactured by BASF, a reaction product of2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl and[(C10- to C16-, mainly C12- to C13-alkyloxy)methyl]oxirane), “TINUVIN405” (manufactured by BASF, a reaction product of2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and(2-ethylhexyl)-glycidic acid ester), “TINUVIN 460” (manufactured byBASF,2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine),“TINUVIN 1577” (manufactured by BASF,2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol), “TINUVIN 479”(manufactured by BASF,2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine),“TINUVIN 477” (manufactured by BASF, a ultraviolet absorber having a2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkyloxy-2-hydroxypropyloxy]-5-α-cumylphenyl)-2-triazinebackbone (alkyloxy: longer-chain alkyloxy group such as octyloxy,nonyloxy and decyloxy)).

The content of the triazine-based ultraviolet absorber in the acrylicpressure-sensitive adhesive layer (especially, the acrylicpressure-sensitive adhesive layer of the present invention) (or in anacrylic pressure-sensitive adhesive composition) is preferably from 1 to10 parts by weight, more preferably from 3 to 10 parts by weight, stillmore preferably from 3 to 8 parts by weight, based on 100 parts byweight of the acrylic polymer. The content of 1 part by weight or moreis preferred since the light transmittance at a wavelength of 380 nm canthen be lowered, thereby easily providing excellent ultravioletabsorbency in the pressure-sensitive adhesive layer. The content of 10parts by weight or less is also preferred since the total lighttransmittance and haze of the acrylic pressure-sensitive adhesive layercan then be controlled, thereby easily providing an acrylicpressure-sensitive adhesive layer of high transparency. A large amountof an ultraviolet absorber blended in a pressure-sensitive adhesivelayer may lead to poor compatibility, resulting in precipitation of theultraviolet absorber, to thereby cause lowering the transparency ordeteriorating the pressure-sensitive adhesive properties such asadhesive force.

(Light Stabilizer)

The pressure-sensitive adhesive layer (especially, the acrylicpressure-sensitive adhesive layer of the present invention) preferablycontains a light stabilizer, and particularly preferably contains alight stabilizer together with the ultraviolet absorber described above.The light stabilizer can capture radicals generated in photooxidation tothereby enhance resistance of the pressure-sensitive adhesive layeragainst light (especially, ultraviolet light). The light stabilizer maybe used alone or in combination of two or more kinds thereof.

The light stabilizer is preferably, but not limited to, a hinderedamine-based light stabilizer (HALS). Examples of the hinderedamine-based light stabilizer include a polymerized product of dimethylsuccinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (tradename “TINUVIN 622”, manufactured by BASF), a reaction product of apolymerized product of dimethyl succinate and4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol with N,N′,N″,N′″-tetrakis-(4,6-bis-(buthyl-(N-methyl-2,2,6,6-tetramethylpiperidine-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine(weight ratio thereof is 1:1) (trade name “TINUVIN 119”, manufactured byBASF), a polycondensation product ofdibuthylamine.1,3-triazine.N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamineand N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine ((trade name “TINUVIN2020”, manufactured by BASF),poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazin-2,4-diyl}{2,2,6,6-tetramethyl-4-piperidyl}imino]hexamethylene{(2,6,6-tetramethyl-4-piperidyl)imino}) ((trade name “TINUVIN 944”,manufactured by BASF), a mixture ofbis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate andmethyl-1,2,2,6,6-pentamethyl-4-piperidyl sebacate (trade name “TINUVIN765”, manufactured by BASF),bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (trade name “TINUVIN 770”,manufactured by BASF), a reaction product of decanedioic acidbis(2,2,6,6-tetramethyl-1-(octyloxy)4-piperidinyl)ester(1,1-dimethylethylhydroperoxide)and octane (trade name “TINUVIN 123”, manufactured by BASF),bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]buthylmalonate(trade name “TINUVIN 144”, manufactured by BASF), a reaction product of2-aminoethanol with a reaction product of cyclohexane andN-buthyl-2,2,6,6-tetramethyl-4-piperidineamine-2,4,6-trichloro-1,3,5-triazineperoxide (trade name “TINUVIN 152”, manufactured by BASF), a mixture ofbis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate andmethyl-1,2,2,6,6-pentamethyl-4-piperidyl sebacate (trade name “TINUVIN292”, manufactured by BASF).

The content of the light stabilizer (especially, the hinderedamine-based light stabilizer) in the acrylic pressure-sensitive adhesivelayer (especially, the acrylic pressure-sensitive adhesive layer of thepresent invention) (or in an acrylic pressure-sensitive adhesivecomposition) is not particularly limited, but is preferably, forexample, from 0.1 to 3 parts by weight, more preferably from 0.1 to 1parts by weight, based on 100 parts by weight of the acrylic polymer.The content of the light stabilizer of 0.1 part by weight or more ispreferred since resistance against light is then easily exhibited. Thecontent of the light stabilizer of 3 parts by weight or less is alsopreferred since coloring by the light stabilizer itself is then lesslikely to occur, thereby easily providing a pressure-sensitive adhesivelayer having a high total light transmittance and a low haze.

(Crosslinking Agent)

The pressure-sensitive adhesive layer (especially, the acrylicpressure-sensitive adhesive layer of the present invention) may containa crosslinking agent in terms of providing sufficient adhesivereliability to an adherend. For example, the acrylic polymer in theacrylic pressure-sensitive adhesive layer of the present invention maybe crosslinked to control the gel fraction. The crosslinking agent maybe used alone or in combination of two or more kinds thereof.

The crosslinking agent is not particularly limited, and examples thereofinclude an isocyanate-based crosslinking agent, an epoxy-basedcrosslinking agent, a melamine-based crosslinking agent, aperoxide-based crosslinking agent, an urea-based crosslinking agent, ametal alkoxide-based crosslinking agent, a metal chelate-basedcrosslinking agent, a metal salt-based crosslinking agent, acarbodiimide-based crosslinking agent, an oxazoline-based crosslinkingagent, an aziridine-based crosslinking agent, an amine-basedcrosslinking agent and the like. Among them, the isocyanate-basedcrosslinking agent and the epoxy-based crosslinking agent arepreferable, and the isocyanate-based crosslinking agent is morepreferable.

As the isocyanate-based crosslinking agent (polyfunctional isocyanatecompound), examples thereof include lower aliphatic polyisocyanates suchas 1,2-ethylene diisocyanate, 1,4-butylenediisocyanate and1,6-hexamethylene diisocyanate; alicyclic polyisocyanates such ascyclopentylene diisocyanate, cyclohexylene diisocyanate, isophoronediisocyanate, hydrogenated tolylene diisocyanate and hydrogenated xylenediisocyanate; and aromatic polyisocyanates such as 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethanediisocyanate and xylylene diisocyanate. The isocyanate-basedcrosslinking agent may be, for example, commercially available productssuch as a trimethylolpropane/tolylene diisocyanate adduct (manufacturedby Nippon Polyurethane Industry Co., Ltd., trade name “CORONATE L”), atrimethylolpropane/hexamethylene diisocyanate adduct (manufactured byNippon Polyurethane Industry Co., Ltd., trade name “CORONATE HL”), atrimethylolpropane/xylylene diisocyanate adduct (manufactured by MitsuiChemicals Co., Ltd., trade name “TAKENATE D-110N”).

As the epoxy-based crosslinking agent (polyfunctional epoxy compound),examples thereof include N,N,N′,N′-tetraglycidyl-m-xylenediamine,diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane,1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether,ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,polyethylene glycol diglycidyl ether, polypropylene glycol diglycidylether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether,pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether,sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether,adipic acid diglycidyl ester, o-phthalic diglycidyl ester,triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcin diglycidyl ether,bisphenol-S-diglycidyl ether and an epoxy-based resin having two or moreepoxy groups in the molecule. The epoxy-based crosslinking agent may be,for example, commercially available products such as trade name “TETRADC” manufactured by Mitsubishi Gas Chemical Company, Inc.

The content of the crosslinking agent in the pressure-sensitive adhesivelayer (in particular, the acrylic pressure-sensitive adhesive layer ofthe present invention) is not particularly limited, and is preferably0.001 parts by weight to 10 parts by weight, and more preferably 0.01parts by weight to 5 parts by weight based on 100 parts by weight of theacrylic polymer.

(Silane Coupling Agent)

The pressure-sensitive adhesive layer (in particular, the acrylicpressure-sensitive adhesive layer of the present invention) may includea silane coupling agent for the purpose of improving an adhesionproperty to glass. The silane coupling agent may be used either alone orin combination of two or more thereof.

The silane coupling agent is not particularly limited, and examplesthereof include γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane andN-phenyl-aminopropyltrimethoxysilane are preferably exemplified. As thesilane coupling agent, for example, a commercially available productsuch as trade name “KBM-403” (manufactured by Shin-Etsu Chemical Co.,Ltd.) may be used. Among them, γ-glycidoxypropyltrimethoxysilane ispreferable.

The content of the silane coupling agent in the pressure-sensitiveadhesive layer (in particular, the acrylic pressure-sensitive adhesivelayer of the present invention) (or in the acrylic pressure-sensitiveadhesive composition) is preferably 0.01 parts by weight to 1 part byweight, and more preferably 0.03 parts by weight to 0.5 part by weight,based on 100 parts by weight of the acrylic polymer.

(Other Additive)

In the pressure-sensitive adhesive layer (in particular, the acrylicpressure-sensitive adhesive layer), if necessary, in addition to theultraviolet absorber, light stabilizer, crosslinking agent and silanecoupling agent, additives such as a crosslinking accelerator, atackifying resin (rosin derivative, polyterpene resin, petroleum resin,and oil-soluble phenol), an antiaging agent, a filler, a colorant (dyeor pigment), an antioxidant, a chain-transfer agent, a plasticizer, asoftener, a surfactant and an antistatic agent may be used as long asthe property of the present invention is not impaired.

The formation of the pressure-sensitive adhesive layer (in particular,the acrylic pressure-sensitive adhesive layer of the present invention)is not particularly limited, but the pressure-sensitive adhesive layercan be formed by applying the pressure-sensitive adhesive composition(in particular, the acrylic pressure-sensitive adhesive composition) ona substrate or a release liner, and if necessary, drying and/or curingthe applied pressure-sensitive adhesive composition.

The acrylic pressure-sensitive adhesive composition may be produced, asneeded, by further mixing an additive (for example, an ultravioletabsorber, a light stabilizer or the like) into the acrylic polymer or asolution containing the acrylic polymer.

In the coating of the pressure-sensitive adhesive composition, a knowncoating method can be used. For example, a coater such as a gravure rollcoater, a reverse roll coater, a kiss roll coater, a dip roll coater, abar coater, a knife coater, a spray coater, a comma coater and a directcoater, can be used.

The thickness of the pressure-sensitive adhesive layer (especially, theacrylic pressure-sensitive adhesive layer of the present invention) isnot particularly limited, but is preferably from 10 to 200 μm, morepreferably from 10 to 150 μm, and still more preferably from 10 to 100μm, in terms of controlling the light transmittance and the haze and ofproviding adhesion reliability to a adherend.

A gel fraction (ratio of solvent insoluble matter) of thepressure-sensitive adhesive layer (in particular, the acrylicpressure-sensitive adhesive layer of the present invention) is notparticularly limited, but is preferably 30 wt % to 95 wt % and morepreferably 50 wt % to 95 wt % from the standpoint of the adhesionreliability to an adherend or flexibility of the pressure-sensitiveadhesive layer.

The gel fraction can be measured as an insoluble matter in ethylacetate, and in detail, as a weight fraction (unit: wt %) of aninsoluble matter after the pressure-sensitive adhesive layer is immersedin ethyl acetate at 23° C. for 7 days, with respect to the sample beforeimmersing.

Specifically, the gel fraction (solvent insoluble component) is, forexample, a value calculated by “Method of measuring gel fraction” to bedescribed below.

(Method of Measuring Gel Fraction)

About 0.1 g of the pressure-sensitive adhesive layer is sampled from thepressure-sensitive adhesive sheet, wrapped with a poroustetrafluoroethylene sheet (trade name “NTF1122”, manufactured by NittoDenko Corporation) having an average pore size of 0.2 μm, and it is tiedup with a kite string and at this time, it is measured for the weight,and the weight measured is designated as the weight before immersion.The weight before immersion is the total weight of thepressure-sensitive adhesive layer (pressure-sensitive adhesive layersampled above), the tetrafluoroethylene sheet and the kite string. Thetotal weight of the tetrafluoroethylene sheet and the kite string isalso measured, and this weight is designated as the wrapper weight.

Subsequently, the pressure-sensitive adhesive layer of the presentinvention wrapped with a tetrafluoroethylene sheet and tied up with akite string (hereinafter referred to as the “sample”) is put in a 50ml-volume vessel filled with ethyl acetate, followed by allowing tostand still at 23° C. for 7 days. The sample (after ethyl acetatetreatment) is then taken out of the vessel, and it is transferred to analuminum-made cup, followed by drying in a dryer at 130° C. for 2 hoursto remove ethyl acetate, and it is measured for the weight, and thisweight is designated as the weight after immersion.

The gel fraction is calculated according to the following formula:

Gel fraction(wt %)=((X−Y)/(Z−Y))×100

(wherein X is the weight after immersion, Y is the wrapper weight, and Zis the weight before immersion).

The gel fraction of the acrylic pressure-sensitive adhesive layer can becontrolled by, for example, a monomer composition and a weight averagemolecular weight of the acrylic polymer, a used amount (added amount) ofthe crosslinking agent, and the like.

Preferred specific embodiments for the pressure-sensitive adhesive layerof the present invention to have the characteristics of a total lighttransmittance not less than a predetermined value, a light transmittanceat a wavelength of 380 nm not more than a predetermined value, and ahaze not more than a predetermined value include an acrylicpressure-sensitive adhesive layer containing the above-mentioned acrylicpolymer and the above-mentioned triazine-based ultraviolet absorber.This is because the acrylic polymer and the triazine-based ultravioletabsorber are highly compatible so that the acrylic pressure-sensitiveadhesive layer having high transparency as well as exhibitingultraviolet absorbency can easily be obtained. That is, thepressure-sensitive adhesive sheet of the present invention preferablyincludes an acrylic pressure-sensitive adhesive layer containing atleast the acrylic polymer and the triazine-based ultraviolet absorber interms of high ultraviolet absorbency and high transparency.

In particular, affinity of an acrylic polymer with a triazine-basedultraviolet absorber (especially, a hydroxyphenyl triazine ultravioletabsorber) tends to be enhanced when a monomer component havinghydrophilicity such as the above-mentioned nitrogen atom-containingmonomer and hydroxyl group-containing monomer is used as a monomercomponent forming the acrylic polymer. Preferred specific embodiments ofthe pressure-sensitive adhesive layer of the present invention includean acrylic pressure-sensitive adhesive layer that contains at least: ana acrylic polymer formed from a component including, as essentialmonomer components, an alkyl (meth)acrylate and/or an alkoxyalkyl(meth)acrylate, a monomer containing a nitrogen atom in the molecule anda monomer containing a hydroxyl group in the molecule; and atriazine-based ultraviolet absorber (especially, hydroxyphenyl triazineultraviolet absorber), since compatibility of the acrylic polymer andthe triazine-based ultraviolet absorber is enhanced, thereby more easilyproviding high ultraviolet absorbency and high transparency.

In the acrylic pressure-sensitive adhesive layer of the aboveparticularly preferred specific embodiment, the acrylic polymercontained in the acrylic pressure-sensitive adhesive layer preferablycontains, the alkyl (meth)acrylate and/or the alkoxyalkyl (meth)acrylatein a total of proportions thereof of from 30 to 99 wt % (preferably from50 to 99 wt %, more preferably from 70 to 99 wt %), the nitrogenatom-containing monomer in a proportion of from 1 to 30 wt % (preferablyfrom 3 to 25 wt %, more preferably from 3 to 20 wt %), and the hydroxylgroup-containing monomer in a proportion of from 0.5 to 25 wt %(preferably from 1 to 20 wt %, more preferably from 5 to 20 wt %), basedon the total monomer components (100 wt %) forming the acrylic polymer,in terms of compatibility with the triazine-based ultraviolet absorber(especially, hydroxyphenyl triazine ultraviolet absorber).

The pressure-sensitive adhesive layer of the present invention is notlimited to the above specific embodiments.

As another embodiment, the present invention includes an embodiment of apressure-sensitive adhesive sheet including at least apressure-sensitive adhesive layer containing an acrylic polymer and atriazine-based ultraviolet absorber.

(II) Other Pressure-Sensitive Adhesive Layer

The pressure-sensitive adhesive sheet of the present invention mayinclude a pressure-sensitive adhesive layer other than thepressure-sensitive adhesive layer of the present invention along withthe pressure-sensitive adhesive layer of the present invention. Theother pressure-sensitive adhesive layer includes, but not limited to, aknown or common pressure-sensitive adhesive layer formed from a knownpressure-sensitive adhesive such as an urethane-based pressure-sensitiveadhesive, acrylic pressure-sensitive adhesive, rubber-basedpressure-sensitive adhesive, silicone-based pressure-sensitive adhesive,polyester-based pressure-sensitive adhesive, polyamide-basedpressure-sensitive adhesive, epoxy-based pressure-sensitive adhesive,vinylalkylether-based pressure-sensitive adhesive, and fluorine-basedpressure-sensitive adhesive. The pressure-sensitive adhesive may be usedalone or in combination of two or more kinds thereof.

(III) Substrate

The pressure-sensitive adhesive sheet of the present invention may alsoinclude a substrate. The substrate is not particularly limited, andexamples thereof include various optical films such as a plastic film,an antireflection (AR) film, a polarizing plate and a retardation film.As materials of the plastic film and the like, examples thereof includeplastic materials such as polyester resins such as polyethyleneterephthalate (PET); acrylic resins such as polymethyl methacrylate(PMMA); polycarbonate; triacetyl cellulose (TAC); polysulfone;polyarylate; polyimide; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; ethylene-propylene copolymer; cyclicolefin-based polymer such as trade name “ARTON (cyclic olefin-basedpolymer; manufactured by JSR)” and trade name “ZEONOR (cyclicolefin-based polymer; manufactured by Nippon Zeon Co., Ltd.)”. Theplastic materials may be used either alone or in combination of two ormore thereof. The “substrate” is a part laminated to an adherendtogether with the pressure-sensitive adhesive layer, when thepressure-sensitive adhesive sheet is laminated to the adherend (anoptical member and the like). The separator (release liner) released inthe use (lamination) of the pressure-sensitive adhesive sheet is notincluded in the “substrate”.

The substrate is preferably a transparent substrate. The total lighttransmittance in a visible light wavelength region of the substrate (inaccordance with JIS K7361-1) is not particularly limited, but ispreferably 85% or more, and more preferably 88% or more. The haze of thesubstrate (in accordance with JIS K7136) is not particularly limited,but is preferably 1.5% or less, and more preferably 1.0% or less. Thetransparent substrate may be a PET film or a non-oriented film such astrade name “ARTON”, and trade name “ZEONOR”.

The thickness of the substrate is not particularly limited, but forexample, is preferably 12 μm to 75 μm. The substrate may have a singlelayer shape or multilayer shape. On the surface of the substrate, forexample, a known/general surface treatment such as a physical treatmentsuch as a corona discharge treatment and a plasma treatment, and achemical treatment such as an undercoat treatment, may be properlyperformed.

(IV) Pressure-Sensitive Adhesive Sheet of the Present Invention

As described above, the pressure-sensitive adhesive sheet of the presentinvention includes at least the pressure-sensitive adhesive layer. Thepressure-sensitive adhesive sheet of the present invention may be adouble-sided pressure-sensitive adhesive sheet in which both surfacesthereof are a pressure-sensitive adhesive surface, or may be asingle-sided pressure-sensitive adhesive in which only one surfacethereof is a pressure-sensitive adhesive surface. In addition, thepressure-sensitive adhesive sheet of the present invention may be asubstrateless pressure-sensitive adhesive sheet or may be apressure-sensitive adhesive sheet with sheet. Among them, thesubstrateless pressure-sensitive adhesive sheet is preferable, and thedouble-sided pressure-sensitive adhesive sheet consisting of thepressure-sensitive adhesive layer of the present invention is morepreferable.

When the pressure-sensitive adhesive sheet of the present invention is asubstrateless pressure-sensitive adhesive sheet, examples of thespecific structure include, for example, a double-sidedpressure-sensitive adhesive sheet consisting of a pressure-sensitiveadhesive layer (especially, the pressure-sensitive adhesive layer of thepresent invention) and a double-sided pressure-sensitive adhesive sheetincluding the pressure-sensitive adhesive layer of the present inventionand another pressure-sensitive adhesive layer. When thepressure-sensitive adhesive sheet of the present invention is apressure-sensitive adhesive sheet with a substrate, examples of thespecific structure include a single-sided pressure-sensitive adhesivesheet including the pressure-sensitive adhesive layer of the presentinvention on one side of the substrate, a double-sidedpressure-sensitive adhesive sheet including the pressure-sensitiveadhesive layers of the present invention on both sides of the substrate,and a double-sided pressure-sensitive adhesive sheet including thepressure-sensitive adhesive layer of the present invention on one sideof the substrate and the other pressure-sensitive adhesive layer on theother side of the substrate.

On the pressure-sensitive adhesive surface of the pressure-sensitiveadhesive sheet of the present invention, the separator (release liner)may be provided until it is used. In the case where thepressure-sensitive adhesive sheet of the present invention is adouble-sided pressure-sensitive adhesive sheet, each pressure-sensitiveadhesive surface may be protected by using separators, respectively, orprotected in such a way that the surface is wound in a roll form byusing one separator of which both sides are release surfaces. Theseparator is used as a protective material of the pressure-sensitiveadhesive layer, and peeled when the pressure-sensitive adhesive layer islaminated to the adherend. In the case where the pressure-sensitiveadhesive sheet of the present invention is a substratelesspressure-sensitive adhesive sheet, the separator functions as a supportof the pressure-sensitive adhesive layer. The separator may not beprovided.

As the separator, any known release paper may be used. The separator maybe, but not particularly limited to, for example, a substrate having arelease treated layer, a low adhesive substrate composed of a fluorinepolymer, or a low adhesive substrate composed of a non-polar polymer. Asthe substrate having the release treated layer, examples thereof includea plastic film or paper whose surface is treated by a release agent suchas silicon type, long-chain alkyl type, fluorine type, and molybdenumsulfide. As the fluorine-based polymer in the low adhesive substratecomposed of fluorine polymer, examples thereof includepolytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylfluoride, polyvinylidene fluoride, atetrafluoroethylene-hexafluoropropylene copolymer and achlorofluoroethylene-vinylidene fluoride copolymer. As the non-polarpolymer, examples thereof include an olefine-based resin (for example,polyethylene, polypropylene and the like). The separator can be formedby using a known/general method. The thickness of the separator is notparticularly limited.

The thickness (total thickness) of the pressure-sensitive adhesive sheetof the present invention is not particularly limited, but is preferably100 μm to 200 μm, more preferably 10 μm to 150 μm, and more preferably10 to 100 μm. The thickness of the separator is not included in thethickness of the pressure-sensitive adhesive sheet of the presentinvention.

The pressure-sensitive adhesive sheet of the present invention can bemanufactured by a known and general manufacturing method of thepressure-sensitive adhesive sheet. In the case where thepressure-sensitive adhesive sheet of the present invention is asubstrateless pressure-sensitive adhesive sheet, the pressure-sensitiveadhesive sheet is obtained by forming the pressure-sensitive adhesivelayer (in particular, the pressure-sensitive adhesive layer of thepresent invention) on the separator (release film) by the aforementionedmethod. In the case where the pressure-sensitive adhesive sheet of thepresent invention includes a substrate, the pressure-sensitive adhesivelayer (in particular, the pressure-sensitive adhesive layer of thepresent invention) may be directly formed on the surface of thesubstrate (direct scan method), or may also be formed on the substrateby forming the pressure-sensitive adhesive layer (in particular, thepressure-sensitive adhesive layer of the present invention) on theseparator and then transferring (laminating) the formedpressure-sensitive adhesive layer to the substrate (transfer method).

The pressure-sensitive adhesive sheet of the present invention has atotal light transmittance not less than a predetermined value, a lighttransmittance at a wavelength of 380 nm not more than a predeterminedvalue, and a haze not more than a predetermined value, and therefore isexcellent in transparency and excellent in ultraviolet absorbency.Accordingly, the pressure-sensitive adhesive sheet of the presentinvention can realize a display device or input device that has anexcellent ultraviolet protection property for a touch panel, a displayelement or the like therein, while retaining optical characteristics,even in the case of using a small amount of or no optical film. Examplesof the display device include, for example, a liquid crystal displaydevice, an organic EL (electroluminescence) display device, a PDP(plasma display panel), and electronic paper. Examples of the inputdevice include a touch panel.

The pressure-sensitive adhesive sheet of the present invention, whichhas the characteristics described above, is preferably used for opticalapplications. That is, the pressure-sensitive adhesive sheet of thepresent invention is preferably an optical pressure-sensitive adhesivesheet, and more specifically, an optical pressure-sensitive adhesivesheet used in an application for laminating optical members each other(an optical member-laminating application) or an application forproducing a product (optical product) in which the optical members areused.

Since the pressure-sensitive adhesive sheet of the present invention isexcellent in ultraviolet absorbency, when a countermeasure againstultraviolet light is required in an optical product containing thepressure-sensitive adhesive sheet of the present invention, there is anadvantage in that members other than the pressure-sensitive adhesivesheet of the present invention do not have to contain an ultravioletabsorber. Additionally, the pressure-sensitive adhesive sheet of thepresent invention is excellent in transparency, and therefore is lesslikely to adversely affect the appearance of the optical productcontaining the pressure-sensitive adhesive sheet of the presentinvention.

The addition of an ultraviolet absorber in members such as an opticalfilm involves very high cost in the case of using a small amount of thefilm. The pressure-sensitive adhesive sheet of the present invention,however, has ultraviolet protection property imparted, thereby notrequiring an ultraviolet absorber added to other optical members such asan optical film. Accordingly, by using the pressure-sensitive adhesivesheet of the present invention, it is possible to easily impartultraviolet absorbing performance with a cost advantage.

The optical member refers to a member having an optical characteristic(for example, a polarized property, a photorefractive property, a lightscattering property, a light reflective property, a light transmittingproperty, a light absorbing property, a light diffractive property, anoptical rotation property and visibility). The optical member is notparticularly limited so long as the optical member is a member havingthe optical characteristic, and a member constituting the device such asdisplay device (image display device) and input device, or a member usedin the device are exemplified, and examples thereof include a polarizingplate, a wave plate, a retardation plate, an optical compensation film,a brightness enhancing film, a light guide plate, a reflective film, ananti-reflective film, a transparent conductive film (e.g. ITO film), adesign film, a decoration film, a surface protective film, a prism,lens, a color filter, a transparent substrate, and a member in whichthese are laminated (collectively referred to as “a functional film” insome cases). Each of the “plate” and the “film” include a plate shape, afilm shape, and a sheet shape, and for example, the “polarizing film”includes a “polarizing plate” and a “polarizing sheet”.

The optical member is not particularly limited, but for example, may bea member composed of glass, acrylic resin, polycarbonate,polyethyleneterephthalate, a metal thin film, or the like (for example,a sheet shape, film shape or plate shape of member). As described above,the “optical member” of the present invention also includes a member (adesign film, a decoration film, a surface protective film or the like)for decoration or protection while maintaining visibility of the displaydevice or the input device as an adherend.

EXAMPLES

The present invention will be described in detail below according toexamples, but the invention is not limited to these examples.

Example 1

Into a separable flask, 63 parts by weight of 2-ethylhexyl acrylate(2EHA), 9 parts by weight of methyl methacrylate (MMA), 15 parts byweight of N-vinyl-2-pyrrolidone (NVP) and 13 parts by weight of2-hydroxyethyl acrylate (HEA), as monomer components, and 175 parts byweight of ethyl acetate as a polymerization solvent were added and themixture was stirred while introducing nitrogen gas for 1 hour. Afterthus removing oxygen within the polymerization system, 0.2 part byweight of 2,2′-azobisisobutyronitrile was added as a polymerizationinitiator, and the temperature was elevated to 63° C. to allow thesystem to react for 10 hours. Thereafter, ethyl acetate was added toprovide a solution of acrylic polymer having solid concentration of 36wt %.

The acrylic polymer in the above acrylic polymer solution had a weightaverage molecular weight of 850,000.

Next, to the above acrylic polymer solution, 0.528 part by weight of anisocyanate-based crosslinking agent (trade name “TAKENATE D110N”,manufactured by Mitsui Chemicals Inc., active ingredient content: 75%),and 0.054 part by weight of a silane coupling agent (trade name“KBM403”, manufactured by Shin-Etsu Chemical Co., Ltd., activeingredient content: 100%), 2.700 parts by weight of an ultravioletabsorber (trade name “TINUVIN 477”, manufactured by BASF, activeingredient content: 80%, hydroxyphenyl triazine ultraviolet absorber),and 0.360 part by weight of a light stabilizer (trade name “TINUVIN123”, manufactured by BASF, active gradient content of 100%), relativeto 100 parts by weight of the acrylic polymer were added and mixed toprovide an acrylic pressure-sensitive adhesive composition.

The acrylic pressure-sensitive adhesive composition was then applied ona release-treated surface of a polyethylene terephthalate separator (PETseparator) which had the release treated surface (trade name “MRF75”,manufactured by Mitsubishi Plastics, Inc.) so that the thickness afterdrying became 50 μm, heated and dried at 60° C. for 1 minute and at 140°C. for 1 minute, further subjected to aging at 23° C. for 120 hours toprovide a pressure-sensitive adhesive sheet (a substratelesspressure-sensitive adhesive sheet having a structure of acrylicpressure-sensitive adhesive layer/release film).

Comparative Example 1

An acrylic polymer solution was obtained in the same manner as inExample 1.

Next, to the acrylic polymer solution, 0.528 part by weight of anisocyanate-based crosslinking agent (trade name “TAKENATE D110N”,manufactured by Mitsui Chemicals Inc., active ingredient content: 75%)and 0.054 part by weight of a silane coupling agent (trade name“KBM403”, manufactured by Shin-Etsu Chemical Co., Ltd., activeingredient content: 100%), relative to 100 parts by weight of theacrylic polymer were added and mixed to provide an acrylicpressure-sensitive adhesive composition.

Using the pressure-sensitive adhesive composition, a pressure-sensitiveadhesive sheet (a substrateless pressure-sensitive adhesive sheet havinga pressure-sensitive adhesive layer on one side of a release film) wasthen obtained in the same manner as in Example 1.

(Measurements)

The following measurements were performed for the pressure-sensitiveadhesive sheets obtained in Example and Comparative Example. The resultsare shown in Table 1.

(1) Haze

The pressure-sensitive adhesive layer surface of the pressure-sensitiveadhesive sheet was laminated to a slide glass (trade name “MICRO SLIDEGLASS”, model “S”, manufactured by Matsunami Glass Ind., Ltd.,thickness: 1.3 mm, total light transmittance: 91.8%, haze: 0.1%, groundedges), and was allowed to stand under an environment of a temperatureof 23° C. and humidity of 50% RH for 30 minutes. After that, the releasefilm was removed to provide a test piece.

The haze of the test piece was measured using a haze meter (trade name“HM-150”, manufactured by Murakami Color Research Laboratory Co., Ltd.)in an environment of 23° C. and 50% RH.

The measurement of the haze was performed according to JIS K 7136.

(2) Total Light Transmittance (Light Transmittance at a Wavelength of400 to 780 nm (Visible Light)) and Light Transmittance at a Wavelengthof 380 nm

The pressure-sensitive adhesive layer surface of the pressure-sensitiveadhesive sheet was laminated to a slide glass (trade name “MICRO SLIDEGLASS”, model “S”, manufactured by Matsunami Glass Ind., Ltd.,thickness: 1.3 mm, total light transmittance: 91.8%, haze: 0.1%, groundedges), and allowed to stand under an environment of a temperature of23° C. and humidity of 50% RH for 30 minutes. After that, the releasefilm was removed to provide a test piece.

The light transmittances at respective wavelengths of the test piece wasmeasured using a haze meter (trade name “HM-150”, manufactured byMurakami Color Research Laboratory) under an environment of 23° C. and50% RH.

The measurement of the light transmittance was performed according toJIS K 7361-1.

(3) Adhesive Force (180° Peeling Adhesive Force)

The pressure-sensitive adhesive layer surface of the pressure-sensitiveadhesive sheet was lined by laminating to a backing substrate and cut toa size of 20 mm in width and 100 mm in length to provide a test piece.

The release film was removed from the test piece, and the test piece waspressure-bonded to an adherend (a glass plate or a PET film) by moving a2 kg roller back and forth once, and subjected to aging under atmosphereof 23° C. and 50% RH for 30 minutes.

After that, the adhesive force (180° peeling adhesive force) (N/20 mm)was measured according to JIS Z0237 (2000) by peeling the test piecefrom the adherend under a condition of a tensile speed of 300 mm/min anda peeling angle of 180 degree using a tensile tester (trade name “TG-1kN), manufactured by Minebea Co., Ltd.) under atmosphere of 23° C. and50% RH.

The glass plate used above was a soda-lime glass (manufactured byMatsunami Glass Ind., Ltd.) and the PET film used above was a PET film(trade name,”LUMIRROR-S-10#100”, manufactured by Toray Industries,Inc.).

As the backing substrate, a PET film (trade name,”LUMIRROR-S-10#25”,Method of measuring gel fraction Toray Industries, Inc.) was used whenthe adhesive force to a glass plate was to be measured, and a PET film(trade name,”A4100”, manufactured by Toyobo Co, Ltd., a PET filmsurface-treated to attain easy adhesion, thickness: 125 μm) was usedwhen the adhesive force to a PET film was to be measured.

(4) Gel Fraction

The gel fraction was determined by the method described above (Method ofmeasuring gel fraction).

(5) b* Value (b* Value in L*a*b* Color System)

The pressure-sensitive adhesive layer surface of the pressure-sensitiveadhesive sheet was laminated to a slide glass (trade name “MICRO SLIDEGLASS”, model “S”, manufactured by Matsunami Glass Ind., Ltd.,thickness: 1.3 mm, total light transmittance: 91.8%, haze: 0.1%, groundedges), and was allowed to stand under an environment of a temperatureof 23° C. and humidity of 50% RH. After that, the release film wasremoved to provide a test piece.

The b* value of the test piece was measured using a simplifiedspectrophotometric colorimeter (trade name “DOT-3C” manufactured byMurakami Color Research Laboratory Co., Ltd.).

The measurement of the b* value was performed according to JIS K 8729.

The b* value of 2.0 or less is less likely to adversely affect theappearance of the product in which the pressure-sensitive adhesive tapeis used, and therefore is preferred.

TABLE 1 Comparative Example 1 Example 1 Thickness [μm] 50 50 Haze [%]0.4 0.2 Total light transmittance [%] 92.1 92.4 Light transmittance at awavelength 0.01 91.7 of 380 nm [%] Adhesive force To glass 13.4 12.4[N/20 mm] To PET 9.9 10.6 Gel fraction [wt %] 84.9 90.7 b* value 1.230.23

For the pressure-sensitive adhesive sheet obtained in Example 1 andComparative Example 1, the light transmittances at respectivewavelengths in the range of from 280 to 780 nm were determined in thesame manner as in the aforementioned “(2) Total light transmittance(Light transmittance at a wavelength of 400 to 780 nm (visible light))and light transmittance at a wavelength of 380 nm”. The results thereofare shown in FIG. 1.

(Reference Test for Compatibility Between Acrylic Polymer andUltraviolet Absorber)

An example of the reference experiment for compatibility of an acrylicpolymer and an ultraviolet absorber is shown below.

Pretest for Compatibility

Monomer components (2-methoxyethyl acrylate (2MEA), 2-ethylhexylacrylate (2EHA), 4-hydroxybutyl acrylate (4HBA), ethyl acrylate (EA),methyl methacrylate (MMA), N-vinyl-2-pyrrolidone (NVP), and/or2-hydroxyethyl acrylate (HEA)) were selected so that the compositionratio of monomers shown in Table 2 below was attained, to provide amonomer mixture solution of 100 parts by weight of the monomercomponents in 200 parts by weight of ethyl acetate as a polymerizationsolvent.

The monomer mixture solution was added in a separable flask and stirredfor 1 hour while introducing nitrogen gas. After thus removing oxygenwithin the polymerization system, 0.2 part by weight of2,2′-azobisisobutyronitrile was added as a polymerization initiator, andthe temperature was elevated to 63° C. to allow the system to react for10 hours. Thereafter, ethyl acetate was added to provide a polymersolution having a solid concentration of 36 wt % (a polymer solution ofthe polymer A, a polymer solution of the polymer B, or a polymersolution of the polymer C).

Next, 4 parts by weight of an ultraviolet absorber was added to thepolymer solution, which was stirred to determine the presence or theabsence of cloudiness by visual observation.

When the cloudiness did not occur, the compatibility was rated as“good”, and when the cloudiness occurred, the compatibility was rated as“poor”.

The results are shown in Table 3.

TABLE 2 Polymer Monomer composition ratio (by weight) Polymer A2MEA/2EHA/4HBA = 50/49/1 Polymer B 2MEA/EA/MMA/4HBA = 66/23/10/1 PolymerC 2EHA/MMA/NVP/HEA = 63/9/15/13

TABLE 3 Ultraviolet Solubility absorbency in Polymer Shorter LongerPoly- Poly- Poly- wave- wave- mer mer mer Ultraviolet absorber lengthlength A B C Tinuvin 326(benzotriazole good good — poor good UVabsorber) Tinuvin 477(hydroxyphenyl- good good poor poor good triazineUV absorber) Tinuvin 384-2(benzotriazole good poor — good good UVabsorber) Tinuvin 479(hydroxyphenyl- good good — poor good triazine UVabsorber) Chimassorb 81(benzophenone good poor — good good UV absorber)Tinuvin 109(benzotriazole good poor — good good UV absorber) Sumisorb130(benzophenone good poor — good — UV absorber) Sumisorb300(benzotriazole good good — poor — UV absorber) Sumisorb350(benzotriazole good poor — poor — UV absorber) Tinuvin400(hydroxyphenyl- good poor — good good triazine UV absorber) TinuvinPS(benzotriazole good poor — good good UV absorber) Tinuvin405(hydroxyphenyl- good poor — good good triazine UV absorber)

In Table 3, the “shorter wavelength” means “light having a wavelength of330 nm” and the “longer wavelength” means “light having a wavelength of380 nm”. The “good” in the columns of the ultraviolet absorbency shows agood light absorbency, and the “poor” shows a poor light absorbency.

The “-” in Table 3 shows that the evaluation was not performed.

The abbreviations in Table 3 means the followings.

Tinuvin 326: benzotriazole ultraviolet absorber (trade name “TINUVIN326”, manufactured by BASF)

Tinuvin 477: hydroxyphenyltriazine ultraviolet absorber (trade name“TINUVIN 477”, manufactured by BASF)

Tinuvin 384-2: benzotriazole ultraviolet absorber (trade name “TINUVIN384-2”, manufactured by BASF)

Tinuvin 479: hydroxyphenyltriazine ultraviolet absorber (trade name“TINUVIN 479”, manufactured by BASF)

Chimassorb 81: benzophenone ultraviolet absorber (trade name “CHIMASSORB81”, manufactured by BASF)

Tinuvin 109: benzotriazole ultraviolet absorber (trade name “TINUVIN109”, manufactured by BASF)

Sumisorb 130: benzophenone ultraviolet absorber (trade name “SUMISORB130”, manufactured by Sumitomo Chemical Company, Limited)

Sumisorb 300: benzotriazole ultraviolet absorber (trade name “SUMISORB300”, manufactured by Sumitomo Chemical Company, Limited)

Sumisorb 350: benzotriazole ultraviolet absorber (trade name “SUMISORB350”, manufactured by Sumitomo Chemical Company, Limited)

Tinuvin 400: hydroxyphenyltriazine ultraviolet absorber (trade name“TINUVIN 400”, manufactured by BASF)

Tinuvin PS: benzotriazole ultraviolet absorber (trade name “TINUVIN PS”,manufactured by BASF)

Tinuvin 405: hydroxyphenyltriazine ultraviolet absorber (trade name“TINUVIN 405”, manufactured by BASF)

Example 1 above was performed using polymer C and a ultraviolet absorber(trade name “TINUVIN 477”, hydroxyphenyl triazine ultraviolet absorbermanufactured by BASF), which is a combination exhibiting a goodcompatibility between the acrylic polymer and the ultraviolet absorber.

As shown in Table 3, it can be readily presumed that, besides thecombination of the acrylic polymer and the ultraviolet absorber used inExample 1, a certain combination of an acrylic polymer and anultraviolet absorber, which shows a good solubility, exhibits the sameeffect as in Example 1. That is, those skilled in the art can practicethe present invention even with a combination other than the specificcombination described in Example 1 from the above results.

(Reference Test)

For pressure-sensitive adhesive sheets, the following light resistancetest was performed to evaluate the light resistance thereof. Also, withrespect to the light resistance, effects of a light stabilizer on thelight resistance were shown. Upon the light resistance test,pressure-sensitive adhesive sheets of Examples 2 to 6 were furtherproduced. The results of the test are shown in Table 4.

Example 2

A pressure-sensitive adhesive sheet (a substrateless pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer on one side ofa release film) was obtained in the same manner as in Example 1, exceptthat the acrylic pressure-sensitive adhesive composition was applied sothat the thickness after drying became 12 μm.

Example 3

A pressure-sensitive adhesive sheet (a substrateless pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer on one side ofa release film) was obtained in the same manner as in Example 2, exceptthat the light stabilizer (trade name “TINUVIN 123”, manufactured byBASF) was not added to the acrylic polymer solution.

Example 4

A pressure-sensitive adhesive sheet (a substrateless pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer on one side ofa release film) was obtained in the same manner as in Example 2, exceptthat an antioxidant (trade name “IRGANOX 1010”, manufactured by BASF)was used instead of the light stabilizer (trade name “TINUVIN 123”,manufactured by BASF).

Example 5

A pressure-sensitive adhesive sheet (a substrateless pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer on one side ofa release film) was obtained in the same manner as in Example 2, exceptthat the amount of the light stabilizer (trade name “TINUVIN 123”,manufactured by BASF) was changed to 0.720 part by weight.

Example 6

A pressure-sensitive adhesive sheet (a substrateless pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer on one side ofa release film) was obtained in the same manner as in Example 2, exceptthat the amount of the light stabilizer (trade name “TINUVIN 123”,manufactured by BASF) was changed to 1.080 parts by weight.

Light Resistance Test

The pressure-sensitive adhesive layer surface of the pressure-sensitiveadhesive sheet was laminated to PET film (trade name “LUMIRROR S-10#25”,manufactured by Toray Industries), was cut to a size of 20 mm in widthand 100 mm in length and was allowed to stand under an environment of atemperature of 23° C. and humidity of 50% RH for 30 minutes to provide alaminate (a laminate of PET film/acrylic pressure-sensitive adhesivelayer/release film).

The laminate was loaded on a sunshine carbon arc weatherometer (tradename “WEL-3SUN-H”, manufactured by Suga Test Instruments Co., Ltd.) andirradiated with light to start the test. The time point of starting theweathering test was set as the “initial time” of the weathering test.

Elongations (breaking elongations) were determined by the elongationtest (breaking elongation test) described below at the “initial time”,“200 hours after starting the test” (after 200 hours), “500 hours afterstarting the test (after 500 hours), and “1000 hours after starting thetest” (after 1000 hours). The results are shown in Table 4.

Occurrence of deterioration of the PET film and degree thereof can beestimated from the elongations at those times, and weather resistance ofthe pressure-sensitive adhesive sheet was estimated from the occurrenceof the film deterioration and the degree thereof. This estimation isbased on the presumption that a good whether resistance causes a smalldeterioration of PET film, and a poor whether resistance causes a largedeterioration of PET film.

Elongation Test (Breaking Elongation Test)

Elongations (breaking elongations) (%) were determined using a tensiletester (trade name “TG-1 kN”, manufactured by Minebea Co., Ltd.)according to the tensile strength and elongation sections in JIS K 6767.

The test pieces upon conducting the elongation test have a laminatestructure of PET film/pressure-sensitive adhesive layer, which is astructure obtained by excluding the release film from theabove-mentioned laminate (the laminate of PET film/pressure-sensitiveadhesive layer/release film).

TABLE 4 Example 2 3 4 5 6 Breaking Initial time 150 150 150 150 150elongation After 200 hr 122 100 140 — — [%] After 500 hr 97 5 14  75  82After 1,000 hr 94 7 37 — —

From the above results, it was able to be confirmed that the addition ofa light stabilizer enhanced the weather resistance (the resistanceagainst light).

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

This application is based on Japanese Patent Application No. 2011-216301filed on Sep. 30, 2011, the entire subject matter of which isincorporated herein by reference.

The present invention provides the following pressure-sensitive adhesivesheet.

(1) A pressure-sensitive adhesive sheet, having:

-   -   a total light transmittance of 85% or more;    -   a light transmittance at a wavelength of 380 nm of 5% or less;        and    -   a haze of 3% or less.

(2) The pressure-sensitive adhesive sheet according to (1), comprising apressure-sensitive adhesive layer containing an acrylic polymer and atriazine-based ultraviolet absorber.

(3) The pressure-sensitive adhesive sheet according to (2), wherein theacrylic polymer contains, as a monomer unit, at least one of an alkyl(meth)acrylate having a linear or branched alkyl group and analkoxyalkyl (meth)acrylate.

(4) The pressure-sensitive adhesive sheet according to (3), wherein atotal of a proportion of the alkyl (meth)acrylate and a proportion ofthe alkoxyalkyl (meth)acrylate is 30 wt % or more based on total monomercomponents (100 wt %) forming the acrylic polymer.

(5) The pressure-sensitive adhesive sheet according to any one of (2) to(4), wherein the acrylic polymer contains, as a monomer unit, a monomercontaining a nitrogen atom in a molecule thereof.

(6) The pressure-sensitive adhesive sheet according to (5), wherein aproportion of the monomer containing a nitrogen atom in a moleculethereof is 1 to 30 wt % based on total monomer components (100 wt %)forming the acrylic polymer.

(7) The pressure-sensitive adhesive sheet according to any one of (2) to(6), wherein the acrylic polymer contains, as a monomer unit, a monomercontaining a hydroxyl group in a molecule thereof.

(8) The pressure-sensitive adhesive sheet according to (7), wherein aproportion of the monomer containing a hydroxyl group in a moleculethereof is 0.5 to 25 wt % based on total monomer components (100 wt %)forming the acrylic polymer.

(9) The pressure-sensitive adhesive sheet according to any one of (2) to(8), wherein a content of the triazine-based ultraviolet absorber is 1to 10 parts by weight relative to 100 parts by weight of the acrylicpolymer.

(10) The pressure-sensitive adhesive sheet according to any one of (1)to (9), which is an optical pressure-sensitive adhesive sheet.

1. A pressure-sensitive adhesive sheet, having: a total lighttransmittance of 85% or more; a light transmittance at a wavelength of380 nm of 5% or less; and a haze of 3% or less, wherein thepressure-sensitive adhesive sheet comprises an acrylic polymer, whereinthe acrylic polymer contains, as a monomer unit, at least one of analkyl (meth)acrylate having a linear or branched alkyl group and analkoxyalkyl (meth)acrylate, and wherein the acrylic polymer contains, asa monomer unit, a monomer containing a hydroxyl group in a moleculethereof.
 2. The pressure-sensitive adhesive sheet according to claim 1,wherein the acrylic polymer is contained in a pressure-sensitiveadhesive layer and the pressure-sensitive adhesive layer furthercontains a triazine-based ultraviolet absorber.
 3. Thepressure-sensitive adhesive sheet according to claim 1, wherein a totalof a proportion of the alkyl (meth)acrylate and a proportion of thealkoxyalkyl (meth)acrylate is 30 wt % or more based on total monomercomponents (100 wt %) forming the acrylic polymer.
 4. Thepressure-sensitive adhesive sheet according to claim 2, wherein theacrylic polymer contains, as a monomer unit, a monomer containing anitrogen atom in a molecule thereof.
 5. The pressure-sensitive adhesivesheet according to claim 4, wherein a proportion of the monomercontaining a nitrogen atom in a molecule thereof is 1 to 30 wt % basedon total monomer components (100 wt %) forming the acrylic polymer. 6.The pressure-sensitive adhesive sheet according to claim 1, wherein aproportion of the monomer containing a hydroxyl group in a moleculethereof is 0.5 to 25 wt % based on total monomer components (100 wt %)forming the acrylic polymer.
 7. The pressure-sensitive adhesive sheetaccording to claim 2, wherein a content of the triazine-basedultraviolet absorber is 1 to 10 parts by weight relative to 100 parts byweight of the acrylic polymer.
 8. The pressure-sensitive adhesive sheetaccording to claim 1, which is an optical pressure-sensitive adhesivesheet.
 9. The pressure-sensitive adhesive sheet according to claim 1,wherein the acrylic polymer contains, as a monomer unit, a monomercontaining a nitrogen atom in a molecule thereof.
 10. Thepressure-sensitive adhesive sheet according to claim 3, wherein theacrylic polymer contains, as a monomer unit, a monomer containing anitrogen atom in a molecule thereof.
 11. The pressure-sensitive adhesivesheet according to claim 9, wherein a proportion of the monomercontaining a nitrogen atom in a molecule thereof is 1 to 30 wt % basedon total monomer components (100 wt %) forming the acrylic polymer. 12.The pressure-sensitive adhesive sheet according to claim 10, wherein aproportion of the monomer containing a nitrogen atom in a moleculethereof is 1 to 30 wt % based on total monomer components (100 wt %)forming the acrylic polymer.
 13. The pressure-sensitive adhesive sheetaccording to claim 1, further comprising a hydroxyphenyl triazine-basedUV absorber.